Preheat the oven to 350 degrees, and set the oven racks at the top and lower-middle
levels.
Line two 12-cavity muffin tins with muffin cups and set aside.

Make the filling: combine the cream cheese, egg, sugar and salt in a bowl,
beating until blended.
Stir in chocolate chips.

Make the cupcakes: In a large bowl, sift together the flour, sugar, cocoa,
baking soda and salt.
Add the water, oil, vinegar and vanilla, beating at medium speed just until
combined.

Fill the prepared muffin cups about 1/3 up. Place about 2 teaspoonsful of the
filling on top of each of these. Bake for 15 to 18 minutes on the top and lower-middle
racks of the oven, then reverse the positions of the two cupcake pans (putting
the one from the top on the lower middle rack and vice versa), and bake another
15 to 18 minutes. Allow to cool completely, then store in an airtight container
for up to 3 days. (Do not freeze, as it gives the cream cheese mixture a funny
texture.)